Japanese Patent No. 4385406 (JP 4385406) discloses a plurality of linear motor units each including a mover and a stator, the mover including a direct drive shaft capable of reciprocating in an axial direction of the shaft and a permanent magnet array mounted to the direct drive shaft, the stator having a plurality of excitation windings each formed of a winding conductor wound in a coil such that the mover reciprocates in an inner space defined inside the excitation windings. The linear motor units are arranged such that the respective direct drive shafts of the liner motor units are juxtaposed in parallel. A back yoke is disposed outside the respective stators of the linear motor units to partly form respective magnetic circuits of the linear motor units. The back yoke is constituted from a plurality of pipes made of magnetic material. The linear motor units provided with the back yoke are supported, being sandwiched between a block frame and a cover.
The manufacturing process of such conventional linear motor is complicated since the back yoke formed of a plurality of pipes must be mounted on a plurality of linear motor units. In addition, a block frame and a cover are necessary to support the linear motor units. Consequently, the linear motor is inevitably large in volume and heavy in weight.